feat(applicant): mentor list + request-change dialog (PR8 Task 7)

- /applicant/mentor renders all co-mentors as cards
- New "Request a mentor change" dialog opens a free-form reason + optional
  per-mentor target; calls mentor.requestChange and shows admin-routed
  confirmation toast
- Pending-request guard disables the button until the admin resolves

src/server/routers/applicant.ts

@@ -1319,9 +1319,10 @@ export const applicantRouter = router({
         mentorAssignments: {
           include: {
             mentor: {
-              select: { id: true, name: true, email: true },
+              select: { id: true, name: true, email: true, expertiseTags: true },
             },
           },
+          orderBy: { assignedAt: 'asc' },
         },
         wonAwards: {
           select: { id: true, name: true },
@@ -1492,6 +1493,17 @@ export const applicantRouter = router({
       logoUrl = await provider.getDownloadUrl(project.logoKey)
     }
 
+    // Does this user have an open mentor-change request for this project?
+    // (Used by the applicant mentor page to disable the "Request a change" button.)
+    const myPendingChangeRequest = await ctx.prisma.mentorChangeRequest.findFirst({
+      where: {
+        projectId: project.id,
+        requestedByUserId: ctx.user.id,
+        status: 'PENDING',
+      },
+      select: { id: true },
+    })
+
     return {
       project: {
         ...project,
@@ -1505,6 +1517,7 @@ export const applicantRouter = router({
       hasPassedIntake: !!passedIntake,
       isIntakeOpen: !!activeIntakeRound,
       logoUrl,
+      hasPendingMentorChangeRequest: !!myPendingChangeRequest,
     }
   }),